1. Field of the Invention
The present invention relates to laser diodes, and more particularly to a laser diode assembly which promotes accurate spacing and alignment of diode bars, cooling of diode bars and electrical conductivity through the diode bars, and facilitates assembly.
2. Background Art
Laser diode arrays are in general used in a wide variety of industrial and research applications. Pluralities of diode bars are mounted on a substrate to provide the multiplied power of numerous bars, versus the effect offered by a single bar. For arrays that are operated in harsh environments such as high temperatures or rapidly changing temperatures it is desired that the entire array assembly be assembled with high temperature solders. In arrays that are fabricated with high temperature solders it is imperative to minimize the stress induced in the laser bar from the assembly process. To optimize the efficiency of a multiple diode bar array the materials used must also have high electrical conductivity and thermal conductivity. This requires the use of different materials that have different thermal expansion properties. In a hard soldered assembly small thermal expansion mismatches can cause stress on the bars and hence reliability issues. In addition good alignment of the bars is necessary to maintain high efficiency, good performance, and high reliability.
Most efforts in the art have focused upon modes and means of mounting numerous diode bars quickly and inexpensively. The mounting of numerous bars into a single array historically has been a somewhat labor and/or cost intensive proposition, thus partially impeding the development of economical products and devices incorporating laser diode arrays.
For example, U.S. Pat. Nos. 5,040,187 and 5,284,790, both to Karpinski, show a “monolithic” laser diode array. These patents teach a substrate having a number of grooves formed therein, and into which the diode bars are inserted. The substrate is flexed into an arc to widen the grooves; the diode bars are inserted into the temporarily widened grooves, after which the substrate is relaxed and allowed elastically to return to its normal shape, which results in an effective narrowing of the grooves thereby to help hold the inserted diodes in place. A variety of “submounts” for the array also are taught. However, the methods and configurations of the disclosures are not conducive to diode bar alignment, as the bars tend to tip and roll within the grooves during assembly.
U.S. Pat. No. 5,128,951 to Karpinski also shows a particular type of laser diode array and method of fabrication. The disclosure has to do with providing an inexpensive mode of manufacturing a diode bar array. A substrate is provided with two layers, an upper conductive layer immediately above and in flush contact with a lower non-conductive layer. The grooves for receiving the diode bars are cut into the substrate so as to completely pierce the upper layer and penetrate into the lower non-conductive layer. The disclosure purports thereby to provide a means for mounting diode bars which promotes conductivity between bars while also providing heat transfer into the lower electrically insulating layer. The maximized alignment of the bars in the grooves also is not taught.
U.S. Pat. No. 5,305,344 to Patel discloses a laser diode array. This disclosure teaches diversity in diode bar packing, and a configuration which possibly eases the replacement of defective individual bars, but is comparatively complex and expensive.
U.S. Pat. No. 5,311,535 to Karpinski shows a laser diode array which provides for laser emission from the minor surfaces of the diode bars. The device involves the disposition of diode bars into a grooved substrate. Diode bar alignment is not carefully optimized.
Other United States patents of interest in the field include U.S. Pat. No. 6,295,307 to Hoden; U.S. Pat. No. 5,644,586 to Kawano et al.; U.S. Pat. No. 5,627,850 to Irwin et al.; U.S. Pat. No. 5,568,498 to Nilsson; U.S. Pat. No. 5,497,391 to Paoli; U.S. Pat. No. 5,418,799 to Tada; U.S. Pat. No. 5,440,577 to Tucker; U.S. Pat. No. 5,394,426 to Joslin; U.S. Pat. No. 5,212,707 to Heidel et al.; U.S. Pat. No. 5,105,430 to Mundinger et al.; U.S. Pat. No. 5,031,187 to Orenstein et al.; U.S. Pat. No. 5,061,974 to Onodera et al; U.S. Pat. No. 5,060,237 to Peterson; U.S. Pat. No. 4,980,893 to Thornton et al.; U.S. Pat. No. 4,947,401 to Hinata et al.; U.S. Pat. No. 4,903,274 to Taneya et al.; U.S. Pat. No. 4,881,237 to Donnelly; and U.S. Pat. No. 4,092,614 to Sakuma et al.
Nevertheless, a need remains for a means and method of providing a laser diode array which at once is simple and economical that can operate in harsh environments, and yet provide reliable operation, optimized diode bar alignment to promote emission efficiency without sacrificing efficient electrical conductivity between, and cooling of, the diode bars.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
The foregoing discussion of the prior art derives primarily from U.S. Pat. No. 6,352,873 to Hoden who discloses a method for assembling a diode bar assembly by locating a first conductive spacer on a planer working surface; disposing a first solder preform on the first conductive spacer; placing a diode bar on the first solder preform; disposing a second solder preform on the diode bar; placing a second conductor spacer on the second solder preform; compressing the spacers, preforms and diode bar parallel together; heating the solder preforms above their melting temperatures, and allowing the melted solder preforms to harden by cooling.